Project summary Patients with Multiple Endocrine Neoplasia type 1 (MEN1) almost invariably develop multiple duodenopancreatic neuroendocrine tumors (dpNETs), but only a subset progress to metastasis. Currently, we lack the ability to identify those patients at high risk of developing aggressive and metastatic disease. Surgical resection is the only curative option when dpNETs are localized, and is associated with significant morbidity. There is a critical unmet need for molecular, actionable features associated with the development of metastatic dpNETs that provide for markers of risk stratification, or represent therapeutic targets. Our long-term goals are to develop a liquid biopsy approach to identify patients with MEN1-related dpNETs that are at high risk of developing distant metastasis and to develop novel targeted therapies to prevent metastasis. The overall objective of this study is to identify actionable signatures of pNET progression by performing integrated multi- omic profiling of longitudinally collected plasma-, plasma-derived exosomes and tissue from a mouse model of MEN1-pNET and of retrospective blood samples from patients with MEN1-related dpNETs. To address this objective, we propose two specific aims. In Specific Aim 1 we will collect longitudinal plasma, plasma-derived exosomes, and tissue samples from a Men1fl/flPdx1-CreTg mouse model of MEN1-pNET and, using these biospecimen, perform mass spectrometry based metabolomic, proteomic and immune complex profiling to identify signatures associated with disease development and progression. In Specific Aim 2 we will identify blood- based signatures associated with metastatic disease in human samples of MEN1-related dpNET. This will be accomplished by untargeted metabolomic, proteomic and immune complex profiling of blood in a retrospective cohort of MEN1 patients with dpNETs with distant metastases (cases; n=15); MEN1 patients with dpNETs without distant metastases (n=30), and MEN1 patients without dpNETs (n=15). Blinded validation of identified biomarkers will be performed in a second equally sized independent patient cohort. This unique collaboration takes advantage of state-of-the-art mass spectrometry technology, a disease relevant genetic mouse model of MEN1-related pNET as well as blood samples from three well-characterized MEN1 cohorts from expert centers in the US and Europe with the sole objective of identifying actionable features that may offer utility for risk stratification or provide therapeutic targets. This project is significant because it aims to address an unmet clinical need by identifying blood-based biomarkers associated with disease progression and metastasis in patients with MEN1-related dpNETs as well as identifying a set of tumor antigens associated with dpNETs that may be harnessed for the subsequent development of vaccines for subjects at risk and/or as targets for immunotherapeutic applications. This approach opens new horizons for risk-stratification and exploration of novel therapeutic targets in MEN1-related dpNETs. As over 40% of sporadic pNETs carry somatic MEN1-mutations, these findings can also be relevant to this broader patient population.